Generally, styrenic resins can have good transparency, heat stability and mechanical properties and have accordingly been widely used. In particular, flameproof rubber modified styrenic resins can be used to produce housings for electric/electronic goods because of their desirable properties. In order to provide styrenic resins with mechanical strength, rubber components are typically added. Further, bromic flame retardants and antimony trioxide are typically added to obtain flame retardancy. However, these resin compositions in which a flame retardant is added may have poor color development due to the difference in refractive index between the flame retardant and the styrenic resin.
In order to solve the above problems, antimony trioxide having a small size of about 0.02 to 0.1 μm, antimony pentoxide having a small size of about 0.02 to 0.1 μm instead of antimony trioxide, or a combination of conventional antimony trioxide and fine particles of antimony pentoxide have been commonly used.
However, the above methods may have limited applicability because these methods all employ antimony oxide fine particles. So, it is necessary to develop new techniques that can easily improve color development or colorability.
Polyester resins typically have a structure including short chains, and thus may not bend easily. Accordingly, polyester resins can have good rigidity, electrical properties, weather resistance, heat resistance, and the tensile strength of polyester resins may not be affected even after long term exposure to high temperatures. Further, crystalline polyester resins have good resistance to various oils, such as diesel oil.
However, the properties of polyester resins can degrade when they are exposed to acid or alkali for a long time at a high temperature due to ester bonds in the polyester chain. Thus, reinforcing agents such as glass fiber can be added to the polyester resins when polyester resins are employed as a structural material. If reinforcing agents are not added, it is difficult to use polyester resins as a structural material produced by injection molding.
It can be particularly difficult to impart flame retardancy to polyester resin because of flame dripping due to very rapid degradation of the polymer during combustion. Accordingly, in order to obtain flame retardancy, reinforcing agents such as glass fiber are added to polyester resin, because polyester resin alone is not flame retardant.